After debugging my MATLAB code, I'd like to be able to turn off assertions to get a bit of extra speed if possible. (The expression inside the assertion is very short and quick, but there are a lot of calls inside tight loops, so it adds up. Yes, I profiled.) How do I do that globally in MATLAB? I'm looking for something akin to defining NDEBUG in C/C++, or enabling optimization in Python, or -disableassertions flag in Java. Find/replace of assert( with %assert( is too ugly for my taste.
1 Answer
It occurred to me after posting these solutions that while effectively disabling assertions, they don't prevent execution of the expression. Perhaps you could exploit short-circuiting of logical expressions (true || expr) to avoid evaluating expr. This could be done by using a global NDEBUG in place of that true. That is, use assert(NDEBUG || expr) so that expr won't be evaluated when NDEBUG is true. For example,
% parentCode.m (or typed on command prompt) global NDEBUG; NDEBUG=true; testassertions % test script below % testassertions.m global NDEBUG if isempty(NDEBUG), NDEBUG=false; end assert(NDEBUG || fprintf('NO\n')==2) % did fprintf write 3 characters? (no, 4) disp('Assertions are off!') To use this approach, you would oviously need to modify your assert calls to use the (NDEBUG || expr) approach, and you would add the two lines to bring in the global, as done in testassertions.m above. This is not the "switch" you are looking for, but it would avoid computing expr, which seems to be the real goal here.
Override with custom assert.m
You can override assert with your own assert.m at the top of your path. Just use varargin and it will work:
function assert(varargin) end The first time you run it or rehash your path, you get a warning, then it's fine!
>> assert(false) >> assert(false,'No error here',[]) >> No errors, no warnings.
Override with anonymous assert
Possibly easier to manage is an anonymous assert function with variable inputs and no outputs:
assert = @(varargin) deal; Here we are using deal with no inputs (nargin=0) because it just does varargout = varargin;.
3 Comments
Nicu Stiurca
So MATLAB has no built-in way to turn off assertions? Bummer. One problem I can see with
assert(NDEBUG || expr, ...), is that I would have to include global NDEBUG in every source file where I want to use this paradigm. I'm starting to think that a simple shell script which comments out/uncomments lines that have an assert is actually a cleaner way to go. Btw, if I override assert with anonymous function, can I un-override it later?
chappjc
It's not the best solution, agreed. However, since it is
global you only need global NDEBUG=false run once per session, either at the command line or in a startup script. It doesn't need to be in every source file, so it is easier than you think. On the topic of anonymous functions, you would just clear the variable that defines the function, but the anonymous solution is less global than a .m file or the global variable option.chappjc
Oh, I see what you mean, to bring in the
global you do need global NDEBUG in every file after you do global NDEBUG; NDEBUG=true.
assert, but I think it gets the job done. Updated answer with details and example.